There are many applications requiring highly isolated yet accurate and rapid measurement of electrical parameters such as voltage, current, frequency and power in a high voltage environment for control and drive purposes or simply for monitoring purposes. An example is electrical drives for railway locomotives that are supplied with electrical current at a voltage of around 3000V. In many of these applications, the measurement signal needs to be transmitted to electronic circuitry in a low voltage environment for control and/or display purposes. It is also desired in certain applications to power the sensor from a power supply situated in the low voltage environment. The transmission of power and signals from a high voltage environment to a low voltage environment requires isolation between the high and low voltage circuit commensurate with the maximum possible voltage difference and applicable standards in order to avoid electrical creep and breakdown.
A sensor for high voltage applications is described in European patent application 1 659 413 in which the measurement signal is transmitted from the high voltage to the low voltage side via an optical fibre transmission, whereas the power supply is transmitted through an isolating transformer system. The isolating transformer comprises three transformer cores interconnected by conductor windings formed by U-shaped terminals mounted on circuit boards having conductive circuit traces interconnecting the ends of the U-shaped terminals in order to close the winding loops. While the sensor according to this prior art has good isolation properties, there is a desire to simplify the construction of the sensor in order to reduce manufacturing cost, increase consistency of isolation properties, reduce defects and the number of faulty parts, and increase reliability of the sensor. It is further a desire to ensure high performance and low measurement error shift over the life time of the sensor.